It has been known for some time to form rollers of roller bearings wherein he rollers are hollow. However, these rollers have primarily been hollow for lubrication purposes. In more recent years, roller bearings have been developed wherein the rollers are formed of resilient material. For example, the patent to Neidhart U.S. Pat. No. 2,842,410, granted July 8, 1958, suggests that the rollers may be formed of resilient material such as rubber and the like. However, the purpose of these rollers bearings was to provide a resilient bearing device having a self-dampening effect.
Several years ago I began to experiment with the substitution of hollow rollers for normal solid rollers in roller bearings. It was my original thought at that time that I could satisfactorily make a roller bearing wherein the desired zero radial clearance was obtained. By providing rollers which were hollow and could flex or flatten out under a slight preload, firm contact could be made by the rollers with both races. This is virtually impossible to obtain with normal roller bearing components in view of the tolerances required in manufacture.
More recently, the patent to Harris, et all, U.S. Pat. No. 3,410,618, granted Nov. 12, 1968, issured. This patent also teaches the use of hollow rollers positioned in a preloaded condition between races of a roller bearing. However, Harris, et al. were primarily interested in anti-skid bearing which could operate at a very high speed and wherein by providing pressure contact of the rollers with the raceways, the resistance to skidding could be improved and an increase in bearing life could be obtained.
Knowing of a particular problem installation, namely the mounting of shafts for grinding wheels wherein runout is critical, experimental roller bearings for production grinding wheel shafts utilizing preloaded hollow rollers were made and installed. It was discovered that not only could the normal runout due to tolerance clearances within the roller bearing be eliminated, but also, it was discovered that runout of the shaft axis due to out of round conditions of the races of the bearing within manufacturing tolerances could be greatly reduced. This was unexpected.
It was further discovered that the quality of the finish of a hollow roller could be much less than that of a solid roller without materially affecting the runout of the axis of the shaft supported by the bearing assembly.
Hereinafter reference will be made to quality of bearings and bearing components. While in many fields there are but superficial standards, the bearing manufacturers, particularly in the U.S., have adopted a set of standards by which bearings are identified and through which bearings of different manufacturers are readily interchangeable in a known manner. These standards have been developed by The Anti-Friction Bearing Manufacturers' Association, Inc. and are known as the AFBMA standards. Basically, these standards are fixed. However, minor revisions are made from time to time wherein the requirements are made more stringent.
The AFBMA standards are divided into a plurality of sections, and it is believed that only Section Nos. 3, 4 and 5 apply to this invention. Attached hereto are Section Nos. 3, 4 and 5 of the AFBMA standards for either retention as a part of the patented file or as an available publication in the Patent Office Scientific Library.
The specific portions of the AFBMA standards are identified as follows:
Section No. 3, Revision No. 9, August, 1967
Section No. 4, Revision No. 6, October, 1966
Section No. 5, Revision No. 5, December, 1962
Section No. 3 of the AFBMA standards refers to the tolerance classification of roller bearings; pages 6, 7, 8 and 9. Bearing are classified as to their accuracy by the tolerance range to which the parts, i.e., (inner and outer race) are manufactured. Tolerance ranges are given in four classes:
ABEC-1 -- has largest tolerance, least accuracy
ABEC-5 -- less tolerance than 1
ABEC-7 -- closer tolerance than 5
ABEC-9 -- has least tolerance, greatest accuracy.